The invention relates to backer board used in wet space construction.
As used herein, a wet space is an interior space normally exposed to splashing, water wash-down, or other wet conditions. In many contexts, the term “wet spaces” typically refers to bathrooms, kitchens, and other interior tiled areas.
Wet space construction seeks to prevent moisture from coming in contact with wooden flooring and wall substrates so as to prevent rot and mold from forming. Rot and mold are largely responsible for substrate deterioration and a wide variety of health issues.
In modern wet space construction, tile or stone floors, walls, and countertops are typically formed by first placing a supportive backer panel over a wood subfloor or directly to wood or metal wall studs. Conventional backer panels (“backer board”) include glass-fiber mesh reinforced cement backer board, fiber-cement backer board, or fiber-reinforced water-resistant gypsum backer board, etc. A waterproofing layer is then applied to the backer panel in the form of a liquid, trowel-applied or sheet membrane to which the tile or stone is then fixed to the waterproofing membrane to form a finished surface. Waterproofing beneath tile or stone is particularly important in multi-story constructions with living spaces beneath the wet space.
Tile is typically bonded to the waterproofing membrane with thin-set mortar. Thin-set mortar is a blend of cement, very finely graded sand, and a water retention compound; it can also include special latex/polymer additives. Thin-set mortar is relatively inexpensive, easy to use, and designed to adhere well in a thin layer—typically not greater than 3/16 inch thick. (The Tile Council of North America, The American National Standards Institute § A118.1 and A118.4 Specifications, last retrieved Mar. 3, 2016, available at https://www.tenatile.com/faqs/64-thinset-mortar.html).
Conventional backer boards for use in wet space construction must provide the necessary rigidity and flexural strength for tile application. Furthermore, they must have at least one surface to which mortar can be bonded for proper tile application. (Note that in this document the terms rigidity and stiffness are used interchangeably; also, the terms flexural and bending are used interchangeably.)
Conventional backer boards thus have typically consisted of glass-fiber mesh reinforced cement backer boards, fiber-cement backer boards, or fiber-reinforced water-resistant gypsum backer boards, etc., all of which are strong and rigid materials. However, conventional backer boards are permeable to moisture, thereby requiring the installation of a waterproofing membrane between the backer board and the ceramic or stone tile covering. Such boards are heavy and difficult to cut, thus requiring a high degree of trade knowledge, skill, and time to properly install.
For a number of reasons, including consumer preferences for intrinsically waterproof materials used in wet space construction, a desired increase in construction simplicity, and (in some cases) the unavailability of craftsmen who can carry out the conventional methods, the industry is moving toward simplified construction/waterproofing systems and methods that are more reliable and significantly reduce the potential for mold, rot, and mildew.
To facilitate these trends, manufacturers have developed polymer foam backer boards that are (1) intrinsically waterproof, thereby eliminating the need for additional waterproofing steps, (2) extremely lightweight and easy to cut and install, eliminating the need for highly skilled workers, and (3) since they are waterproof, can provide a cost-effective alternative to applying a waterproofing membrane over conventional backer boards. Nonetheless, manufacturing polymer foam backer boards to meet industry standards presents several challenges.
Foam panels typically by themselves lack the necessary flexural strength and stiffness to support a tile application and thus they require an additional structure or “facer” to be applied to the surface(s) of the panel. Relative to the foam panel, facers are typically much thinner and much stiffer (much higher modulus). The outer surface of the facer(s) typically has some kind of coating or additional material applied to provide a mortar-bondable surface for tile adhesion.
Several different materials or combinations of materials have been used for the facers, each with its attendant advantages and challenges. The three most prevalent are 1) paper, with a mortar-bondable fabric, 2) glass-fiber mesh with a mortar-bondable cementitious coating, or coated glass mat (which combines into one the functions of the stiffening facer and the mortar-bondable surface), and 3) polymeric film, with a mortar-bondable fabric.
Paper used as a facer can impart the necessary rigidity to a foam panel, but, in the forms that have to date been made commercially available—thin paper facers applied to both sides of the foam panel—it has the disadvantage of supplying very low flexural strength to the board when compared to conventional backer boards or foam boards that employ glass-fiber mesh and a cement coating. And, historically, paper has performed poorly in wet spaces due to its susceptibility to mold and bacteria growth. The reason for the poor flexural strength performance is rooted in the basic behavior of backer boards (indeed, all board-like structures) when they are subjected to bending loads. When the backer board is bent, one of the facers (the facer on the convex side of the bent board—call it the first facer) enters into a state of tensile stress, and the second facer (the facer on the concave side of the bent board) enters into a state of compressive stress. Note that the magnitude of the tensile stress is essentially equal to the magnitude of the compressive stress. Paper, even thin paper, is relatively strong in tension, so the first facer will support a high board bending load. The facer that is in compression, however, is subject to a structural phenomenon known as buckling. If the facers are thin, then buckling in the second facer can occur even at a low board bending load—much lower than the tensile stress capability of the first facer. Thus, it is found that a backer board with two thin paper facers has a low flexural strength.
Foam board panels that employ a glass-fiber mesh or coated glass mat have the advantage of being strong and rigid, but many require the use of plaster washers to support the panel, especially in framed-wall applications, which adds extra time and cost to their installation. In addition, the glass fibers often cause itching and skin and eye irritation during installation. Also, they have inherently higher water vapor permeability, which precludes them from being used in steam showers unless an additional low-perm waterproofing membrane/vapor retarder is applied over them prior to tile application.
Thin polymeric films, e.g., oriented polystyrene (OPS), offer many advantages for use as facers. They have relatively high tensile strength and high modulus, and thus, if applied in thicknesses of at least 0.003 inch thick, impart the necessary strength and rigidity to a foam panel such that it can support tile application. And because these films are strong and tough, the boards can be installed with ordinary fasteners using jobsite installation practices Films of this type have a low water permeability, making the boards suitable for steam room applications without additional low-perm waterproofing membranes/vapor barriers, and, because they do not contribute to the growth of mold or mildew, they are ideal for use in wet space construction. Polymeric films are, however, inherently difficult to adhesively bond to other materials.
In summary, a need exists for a lightweight, waterproof, mortar-bondable laminated foam composite backer board that employs polymeric film facers that may be reliably manufactured in a real world production environment.
Two U.S. patents—U.S. Pat. No. 5,695,870 by The Dow Chemical Company, and U.S. Pat. No. 8,703,632 by Schlueter-Systems—address foam composite backer boards for use in building construction; Schlueter-Systems for wet-space construction in particular. The inventors in the Dow Chemical patent teach that it is critical that the thermoplastic facer film be laminated to both primary surfaces of the foam panel and that any separation or slipping between the film and foam panel at their interface negates the strengthening effect of the facer film. This finding is consistent with that of other industries; for example, sandwich composite panels (as this type of structure—a low-density core “sandwiched” in between two facers—is generally known) are widely used in aerospace structures where high flexural stiffness, high flexural strength, and low weight are critical. They also teach that “The facer film may be laminated to the present foam board by any conventional method known in the art . . . ” The inventor in the Schlueter-Systems patent teaches that the non-stretchable plastic webs (facers) are to be glued directly to the foam core to provide sufficient bending resistance.
Despite Dow Chemical's assertion in U.S. Pat. No. 5,695,870 that “The facer film may be laminated to the present foam board by any conventional method known in the art . . . ,” and despite Schlueter-Systems' suggestion that the plastic webs (facers) are to be glued directly to the foam core, experience with conventional methods for laminating polymeric films of this type has proven to be disappointing. It has been shown that high strength laminating bonds are indeed possible, but they are inconsistent in quality from one production lot to another. The challenge is rooted in the fact polymeric films of this type are very smooth and, in this range of thickness, very stiff and rigid. They therefore do not lend themselves to conventional processing methods.
One conventional processing method is hot roll lamination. But in this thickness range, the heat required to penetrate the film to activate a heat-activated adhesive layer between the foam core and the film can destroy the foam core.
Other processing methods, e.g., roll or spray coating adhesives onto the facer film prior to laminating, present their own set of challenges because polymeric films, particularly thermoplastics, are very smooth materials lacking mechanical bonding sites.
Producing a textured polymer sheet to form mechanical bonding sites would be expensive, technically difficult, and add too much cost.
A breakthrough in the search for a reliable, consistent bond between the facers and the foam board was achieved when the inventors of the present invention inserted a polyolefin-based fabric between the foam core and a polymeric film. The fabric, which can be a scrim or knitted, woven, or nonwoven fabric, e.g., a 0.75 osy (ounce per square yard)-2.25 osy polypropylene spun bond, provides a field of mechanical bonding sites in the form of a dry, fibrous microstructure that can be enveloped by the adhesive during the facer-to-foam bonding operation.
Again, the skilled person will understand that the fabric serves a functional purpose. A fabric layer that is too thin can be subject to destruction when it comes into contact with a hot or melted polymer during manufacture of the composite. Alternatively, if the fabric is too thin, the adhesive will fill the fabric and thus defeat the purpose of adding the bonding sites. As a third disadvantage, an overly thin fabric can be difficult to handle in an otherwise cost-effective manner. In the same manner an overly thick fabric will preclude sufficient penetration of the adhesive and will leave the fabric as the weak point in the overall composite structure.
Besides providing mechanical bonding sites, the fibrous microstructure of the fabric also increases the fracture toughness of the adhesive bond. “Fracture toughness” is a material science and engineering term that quantifies the ability of a material to resist crack propagation if a crack is present. Glass used in automobile windshields is a familiar example of a material with low fracture toughness. The windshield is able to resist large loads as long as there are no cracks existing in the glass. However, once a crack is formed (often resulting from the impact of a pebble thrown up from the road), the crack propagates very easily, often with very little applied load. Many other materials (ductile metals for example) have high fracture toughness even when a crack is present in the structure, the structure can still carry a large load without additional propagation of the crack. In industries that commonly employ high-performance carbon-fiber composites—aerospace, for example—it has been demonstrated that fibrous reinforcement across the plane of the laminating resin or adhesive significantly increases the interlaminar (that is, between layers) fracture toughness of the material in that region. Similarly, in the backer board with fabric inserted between the polymeric film facers and the foam core, the fibers of the fabric extend across the plane of the adhesive and, therefore, increase the fracture toughness of the adhesive bond. Thus, even if a small region of the film has delaminated from the foam, or perhaps a small region never was well-bonded to the foam, the size of the delamination will not be likely to increase. In this way, increasing the fracture toughness enables robust and reliable manufacturing—the adhesive bonds are much more tolerant of the inevitable imperfections that occur in real-world, high-rate production.
Laminating a fabric to the polymeric film—the process step that occurs before the facer-to-foam bonding operation—can be achieved by common processing methods, e.g., extrusion lamination.
Extensive experimentation has shown that the inserted fabric layer enables a robust facer-to-foam adhesive bond, even in a real-world production environment. Reliable bonds of high strength have been demonstrated when the adhesive fully saturates (wets-out) the fabric layer during the facer-to-foam bonding operation, and similar high-strength bonds have been demonstrated even when the fabric layer is only partially saturated by adhesive. Whether or not the fabric is fully saturated, the fabric's fibers provide paths for the shear and tensile loads to be transferred from the polymeric film of the facer to the adhesive on the foam side of the interface.
Thus, with the insertion of a fabric layer between the polymeric film facer and the foam panel, a laminated backer board for wet-space construction has been invented that is lightweight, stiff, strong, waterproof, and mortar-bondable, and can be reliably manufactured in a real-world production environment.